Mojang already gave a solution, this datapack is no longer needed

A simple datapack that makes custom NBT item outputs possible for the Crafter block.

Right now, the Crafter outputs the knowledge book for any custom crafting recipes added by datapacks. I recommend this datapack be used as a library, to prevent too many armor stands summoning for the same Crafter block in different datapacks.

[​How to add your own recipe coversion]

- To add your own recipes, create a "yourrecipe.mcfunction" in your datapack, and inside it should be something like this.

execute as @s[nbt={ArmorItems:[{tag:{Items:[{Slot:1b,id:"minecraft:INGREDIENT"},{Slot:4b,id:"minecraft:INGREDIENT"},{Slot:7b,id:"minecraft:INGREDIENT"}]}},{},{},{}]}] run tag @s add Craft_Exampleexecute as @s[tag=Craft_Example] if block ~ ~ ~ minecraft:crafter[triggered=true] as @e[type=item,limit=1,distance=..1.1,sort=nearest,nbt={Age:1s,Item:{id:"minecraft:knowledge_book",Count:1b}}] run data merge entity @s {Item:{id:"minecraft:YOURITEM",tag:{YOURNBTHERE}}}

- Modify the code above to your recipe and NBT
- Then run "execute as @e[​type=armor_stand,tag=Crafter] at @s run function yourdp:yourrecipe"

If you know some stuff about datapack & commands, it wouldn't be much a hassle to understand how it works.

The code behind how it works is quite simple really.
- Store the Items data from the Crafter into an armor stand when the Crafter is not activated.
- After it validates the matching recipe with the "ArmorItems:[]", it adds a tag that signals that it has a matching recipe.
- When activated, it will check for a nearby item entity with Age:1s & the knowledge book (It doesn't have to be a knowledge book, it can be anything). It will then insert the NBT data into the item entity.